During a stream where she answered various fan questions on Instagram, Tara Strong told her viewers that Twilight Sparkle won't be returning for generation 5, though she did note that other side projects could use her.

Of course, there is a chance that Twi will be returning with a different voice actress and Tara simply wasn't informed, but for now all we can really do is speculate since Hasbro has been tight lipped about information involving the fifth gen of pony. They have been known to hire alternate VA's for side projects, especially lately with Pinkie's new voice in the 3D shorts.